As a barrier membrane of electrochemical devices such as primary cells, secondary cells, polymer electrolyte fuel cells and the like, a polymer having proton conductivity, namely, a polymer electrolyte is used. For example, polymer electrolytes containing as an effective component an aliphatic polymer having a perfluoroalkylsulfonic acid as a super strong acid in the side chain and a perfluoroalkane in the main chain typically including Nafion (trademark of E.I.DuPont) are conventionally used mainly because of excellent power generation property when used as a membrane material or ion exchange component for fuel cells. However, such a kind of materials are said to have problems such as very high cost, low heat resistance, low membrane strength, leading to less practicality without some reinforcements applied.
Under such conditions, development of a inexpensive polymer electrolyte having excellent properties capable of replacing the above-mentioned polymer electrolyte is being activated recently.
For example, there is suggested a block copolymer having a segment substantially free from an introduced sulfonic acid group and a segment having an introduced sulfonic acid group wherein the former segment is composed of polyether sulfone and the latter segment composed of a repeating unit having an ether bond of diphenylsulfone with biphenol having a sulfonic acid group (Japanese Patent Application Laid-Open (JP-A) No. 2003-031232).
However, the block copolymer as described above is not sufficiently satisfactory as a polymer electrolyte for fuel cells and the like, and copolymers showing more excellent performances are desired.